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Author Topic: What receivers have sychronous detection?  (Read 11057 times)
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ND9B
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« on: April 05, 2012, 09:21:21 PM »

I've been reading about synchronous AM detectors, and I'm intrigued. Where can I find a receiver with a built-in synchronous detector? (I'd rather not go with an outboard unit. And, it must be a separate receiver, not a transceiver.)

BTW, has anyone home-brewed an AM synchronous receiver? For that matter, does anyone home-brew receivers anymore? Lots of transmitters, but I never hear anything about receivers.

Bobby Dipole ND9B
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ke7trp
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« Reply #1 on: April 05, 2012, 11:32:47 PM »

Drake R8, Eton Xm1,  Any SDR radio that is compatible with HDSDR software like Afedri, Soft66lc2, winradio ect. Many receivers have it. 

C
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w3jn
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« Reply #2 on: April 05, 2012, 11:37:23 PM »

Receivers with built-in sync detectors include:

- just about any SDR (Flex, SDRIQ, softrock, etc).  It's done in the software.
- Icom R-75 (although it's horribly done, and needs modifications to make it work correctly)
- WJ HF-1000
- TenTec R-340
-  Yaesu FT-1000MP
- Drake R-7 (quasi-sync, not full sync)
- Drake R-8 series - Drake did it right in these radios
There are others, particularly other ham transceivers, but they don't come immediately to mind.

I've HBed sync detectors and receivers but not both at the same time.  There are others here that have HBed receivers as well.  I'm slowly working on a HB receiver that will include a sync detector.
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ND9B
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« Reply #3 on: April 06, 2012, 10:14:24 AM »

Thanks for the advice, the Drake R8 sounds intriguing. I'm looking to use this receiver with the K7DYY Super Senior. Is there any down side to the synchronous AM detector? I would be using it for typical ham work, i.e. a round table with three or more stations, none of which are exactly on frequency  Cheesy . Would there be any lock-up delays as the QSO is passed around?

In other words, is the synchronous AM detector suitable for the ham environment, or is it for SWL only?

Bobby Dipole ND9B
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WD8BIL
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« Reply #4 on: April 06, 2012, 10:17:55 AM »

Quote
In other words, is the synchronous AM detector suitable for the ham environment...

Yes. Many times it makes a qso where none can be had.
Remember, it can always be turned off.

Better to have it and not need it than to need it and not have it!
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WQ9E
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« Reply #5 on: April 06, 2012, 11:11:52 AM »

Sync really shines when there is distortion from selective fading.  Like those receivers offering selectable sideband choice on AM it allows you to avoid interference from either above or below your operating frequency.  It will also clean up the sound of some poorly adjusted modern transceivers running AM.

But it can be problematic at times.  The lock isn't instantaneous on any of the sync detectors although it is very fast on some of them.  In a normal QSO or roundtable this isn't a problem but I sometimes use my R-8 when operating as a net control station and I leave sync off for that because it can lead to the loss of a short comment or part of a call sign as it is locking up.  Sync detectors with very fast lockup tend to be more prone to another issue with sync detection and that is when the sync lock switches from the station of interest to a much stronger signal also in the pass band.

I have several radios with sync detection including some older Grundig and Sony portables along with a Drake R-8, SW-2, and SW-8.  My favorite sync detector is in my Eton E1-XM as it seems the best behaved with fast locking while remaining resistant to switching lock to a different interfering signal, Drake did most of the design work for this receiver and lockup is faster than the earlier (also Drake engineered) Grundig Satellit 800.  For net control and fast break roundtables I leave the sync detector off and rely upon selectable sideband for interference rejection.
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Rodger WQ9E
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« Reply #6 on: April 06, 2012, 11:40:17 AM »

I've found that during some rapid fire breakin QSO's that I have to turn the Sync Detect off 'cause I miss critical comments as the PLL is pulling in.

Restrictions that limit choices:

  • Your restriction puts off the excellent choice of using the Flex 1500 as just a receiver.  That little unit can also do double duty as a near lab quality spectrum analyzer for either on-air of in the shack for troubleshooting. Jeff W2NBC is quite happy with this combo in his station.
  • You put another restriction - namely no external units - but if you do have a favorite receiver with the ability to pull out the IF such as the SP-600, the Sherwood SE-3 is another excellent choice.   Don, K4KYV and others including me like the performance of the SE-3 plus I get to use a really great receiver in the SP-600.

One advantage of these two choices is that you have the means to mute the receiver system that has Sync Detect.  With the first choice there is a mute provision by using the MOX line (and turn the xmit power to 0). Muting in the case of the second option is obvious - assuming theSP-600, the mute circuit is already there

Al
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ke7trp
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« Reply #7 on: April 06, 2012, 11:49:11 AM »

Here is my experience this morning.  I was in the shack and fired up 15 meters on the Icom 756 Pro.  I heard kc2udz in NJ. I am in AZ.  The signal was weak. Hard copy.  Interferance.  White noise. BC band comming in on 430.

I flipped on the GK500 and HRO60 and took the dog out for some frizbee while I waited for tubes to warm up. 

I came back in and tuned kc2udz in.  The HR060 and PD3S flat out DESTROYS the ICOM. No interference at all.  His audio jumped out of the speaker to FM quality hifi audio and there was little fade. 100% copy.  Back to icom, Crappy audio, White noise and BC station interference.

This is what its all about.  Hard copy AM DX, thousands of miles away.  Pull them out and work them with solid copy with a Sync and a good reciever.

C
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WA1GFZ
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« Reply #8 on: April 09, 2012, 02:12:35 PM »

Racal has an interesting circuit that uses an FM detector to generate the carrier for injection into a mixer. MC1357 driving a MC1496.
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KA0HCP
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« Reply #9 on: April 09, 2012, 03:43:14 PM »

http://www.radio-electronics.com/info/rf-technology-design/am-reception/synchronous-demodulator-demodulation-detector.php

Here is a nice one page description of three common methods of implementing synchronous detection.

b.
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R. Fry SWL
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« Reply #10 on: April 10, 2012, 08:11:26 AM »

My Sony ICF-SW7600GR has synchronous detector capability giving a choice of the upper or lower AM sideband.  Also does well on SSB signals.

http://www.universal-radio.com/catalog/portable/0360.html
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KM1H
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« Reply #11 on: April 10, 2012, 11:07:23 AM »

Ive had good results with variable BFO injection to force a lock or just use a low injection for a bit of added carrier. Of course it requires 2 or 3 hands at times when its a roundtable.

The HRO-60 and 50-1 is arguably the best of AM receivers of the old school tech. Digs deep, detects well, distorts little, and hard to overload due to gain distribution. That 2nd RF stage is just a no gain buffer adding much needed front end selectivity to reject those "artifacts" that plague lesser models. Halli liked to switch the 2nd stage out entirely on the lower 2 bands and Hammy lets it run wide open.

I bet that someone who could find a cheap 60 with poor chassis and cabinet cosmetics could make a few changes to really wake it up. Im just against drilling holes in a real nice one Shocked   Maybe start a thread on the changes.
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ke7trp
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« Reply #12 on: April 11, 2012, 12:54:46 AM »

Carl.  Check out this video of the 60 with the new PD3s.  When I flip it on, you can hear the stations audio jump out of the reciever on the video.  Also.  The deep fades and distortion in the audio is smoothed out.

This combination leaves the Icom 756 pro behind in the dust.

http://youtu.be/ez-QqdLGjeU

It would be fun to modify a 60 but I agree, It woud have to be a real sh*t box to start.

C
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k4kyv
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Don
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« Reply #13 on: April 11, 2012, 09:40:30 AM »

Ive had good results with variable BFO injection to force a lock or just use a low injection for a bit of added carrier. Of course it requires 2 or 3 hands at times when its a roundtable.

The HRO-60 and 50-1 is arguably the best of AM receivers of the old school tech. Digs deep, detects well, distorts little, and hard to overload due to gain distribution. That 2nd RF stage is just a no gain buffer adding much needed front end selectivity to reject those "artifacts" that plague lesser models. Halli liked to switch the 2nd stage out entirely on the lower 2 bands and Hammy lets it run wide open.

I bet that someone who could find a cheap 60 with poor chassis and cabinet cosmetics could make a few changes to really wake it up. Im just against drilling holes in a real nice one Shocked   Maybe start a thread on the changes.

That's how I discovered real live synchronous detection, beyond what I had read about it.  Mine was an old  pre-WW2 HRO, on which I had increased the BFO coupling capacitance to make it receive SSB with less distortion.  Tuned on the BFO one night while trying to locate the  carrier of a weak AM signal lost in heavy QRN.  I was astounded that when I zero-beated the carrier, suddenly the audio, which had been almost inaudible, jumped right out at me.  And, I found that even a puny, weak carrier was enough to force-lock the BFO.  Problem was, that any drift of either receiver or signal more than a couple hundred cps would pull it out of lock.  Receiving in that mode was a tedious process, but something I often used with that receiver. I never could make that work with the 75A4.  I think the BFO is too well isolated from the i.f. output, since they are coupled together through the product detector.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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WQ9E
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« Reply #14 on: April 11, 2012, 10:04:20 AM »

Some of the older Hallicrafters receivers (SX-11, 16, 17) had variable BFO injection via a front panel control as did the RME-4300 and 4350 receivers.  I should try my TMC GPR-90 so see how it does on AM since the BFO locks to CW signals unless the RF gain is carefully controlled. I use the GSB-1 adapter now for CW/SSB but the built in BFO might be useful for AM experimentation.

I found that the sync detector on my R-8 does a good job of cleaning up some signals from modern rigs that are imperfectly adjusted. 
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Rodger WQ9E
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« Reply #15 on: April 11, 2012, 09:22:21 PM »

http://www.radio-electronics.com/info/rf-technology-design/am-reception/synchronous-demodulator-demodulation-detector.php

Here is a nice one page description of three common methods of implementing synchronous detection.

b.

I'm wondering if anyone has explored the hard limiting method? 

Al
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Tom WA3KLR
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« Reply #16 on: April 11, 2012, 09:53:53 PM »

The Sony 2010, out of production for many years, has synchronous detection also.

I have a Drake R-7.  The synchronous detector's b.f.o. port is driven by a limiter stage for AM.  The detector i.c. is a double balanced mixer.  This is a true product detector in SSB/CW mode also.

John JN, why do you call it a quasi-synchronous detector?  Because it does not use a phase-locked loop in the b.f.o. port chain?  The limiter method versus the PLL method each has their advantages and disadvantages, like everything in the design world.

People talk about the synchronous detector as if it was magical.  One nice thing about most designs is that detection with a double balanced mixer or today called a Gilbert cell is that the rectification is active full-wave or in other words extremely linear as opposed to the envelope detector implementation which usually distorts heavily above 65 70 % modulation.  Selective fading distortion can be almost eliminated.
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w3jn
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« Reply #17 on: April 11, 2012, 10:57:14 PM »


John JN, why do you call it a quasi-synchronous detector?  Because it does not use a phase-locked loop in the b.f.o. port chain?  The limiter method versus the PLL method each has their advantages and disadvantages, like everything in the design world.



Because the carrier is not locally-generated.  Hard limiting the carrier and feeding it to a mixer is also called a "homodyne", but it's not a true sync detector. 

I've noticed a definite disadvantage with the R-7's quasi-sync detector on deep and long carrier fades, as compared to a true sync.  The true sync detector will ride these fades out easily.  The true advantage of the quasi-sync detector is there's no loop lockup time (ie a "yoop" when a signal comes up), and there's no loop to get confused and lock on an adjacent carrier.   As you noted all of this needs to be considered in the design world, and a "better" being the enemy of "good enough" line needs to be drawn.

One thing I like about the PLL method is you can open the loop and use the BFO and detector as a SSB/CW product detector.  With the proper I/Q allpass filters and matrix combiner you obtain some Fine Business opposite sideband rejection - useful for AM also when the loop is locked.

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WA1GFZ
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« Reply #18 on: April 13, 2012, 09:45:31 PM »

Racal uses the limiter method in the MC1357. I watched the output as the carrier level drops down. As the carrier goes to the noise floor the noise sidebands get wider so the injection signal gets pretty crappy looking. I wonder if it went through a high Q tank circuit or crystal filter the carrier might be recovered at a lower level. You never get the woop sound because the carrier is always locked to the signal coming through the 1357 FM detector. It would be easy to put a PLL between the 1357 and 1496 with say a XOR gate phase detector so when the carrier goes away the pll output goes to center frequency.
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KM1H
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« Reply #19 on: April 14, 2012, 06:27:41 PM »

Quote
Carl.  Check out this video of the 60 with the new PD3s.


It sure lost all the lows, sounds more like an audio processor.

Id need a better A-B comparison during a signal that has lots of deep fading and on a noisy band.

Something like with HLR here on 7290 during a changing band yesterday. I switched from the SX-28 to a HRO-500 on the SSB position and went from 8 to 5 to 2.5 on the filters as he went almost into the noise at times and an 8 land QSO dead zero beat started to come in. The 500 has an interesting PD and AGC and maintained a steady lock. It also has a notch filter that wont quit....talk about deep. The HRO-60 was setup on another bench and on 20M.
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ke7trp
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« Reply #20 on: April 14, 2012, 06:35:24 PM »

Yes. When the PD3 is inserted, there is a good amount of bass lost. I have grown to like the sound of the PD3 and I use it mainly when the band conditions are poor.  It is very very clear and crisp when on and the HRO of course is a little muddy sounding with little highs with the PD3 off.


C
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